How a bacterial disease moves between elk and cattle

Elk in Banff, Alberta Harry Collins Photography/shutterstock

The spread of the novel coronavirus, COVID-19, from a wildlife market in Wuhan, China, has turned public attention to the risks of disease transmission in places where wildlife and people interact.

This awareness is a good thing, according to Mark Boyce, a professor of ecology in the department of biological sciences at the University of Alberta. “We need to be aware. We need to avoid situations that are likely to result in transmission to humans or to livestock,” says Boyce, whose research lab recently collaborated on a study assessing the risk of disease transmission between elk and grazing cattle in southwestern Alberta grasslands.

Elk and cattle trade many pathogens, including the bacterial disease brucellosis. Introduced to North America via cattle from Europe, brucellosis infected wild bison and elk populations, where it persists. The disease is transmitted through placental fluids. An elk with brucella is likely to abort its first fetus. “The aborted fetus creates curiosity on the part of other elk, as well as cattle,” says Boyce. “They’ll lick it. That’s the most common means of transmission.”

Though brucellosis can cause undulant fever in humans, we prevent its transmission by pasteurizing milk. Other wildlife diseases can seriously harm humans, however. “We don’t have any outbreaks right now,” says Boyce, “but there are a number of diseases that are very serious and there’s a real risk of transmission. We need to be careful.”

The study, led by PhD student Matthieu Pruvot and recently published in the journal Preventive Veterinary Medicine, integrated data on 168 roaming elk and 16 cattle operations and determined that risk of cross-contamination peaks in winter.

“We don’t really have a shortage of habitat,” says Boyce, “but it’s highly seasonal. Cattle are brought out of the high country for calving and to be hay-fed during winter.” Elk, meanwhile, descend from subalpine regions and are then tempted by hay and salt licks in pastures. “Our recommendation is pretty simple: keep salt, water and hay bale feeding near buildings, where elk are hesitant to go.”

In other words, apply common sense in places where human habitat borders that of wildlife, a truth that applies to anyone with cottage property that butts up against a forest or other wild ecosystems. It’s not only people who are at risk; the hazards of interspecies interaction cuts all ways. As the study notes, “Spillover of livestock pathogens into wildlife species…can be a significant threat to the conservation of endangered species.”

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